Directive centimetric antenna



Jan. 13, 1948. A. c. BECK DIRECTIVE CENTIMETRIC ANTENNA Filed Aug. 21,194:5 4 Sheets-Sheet 1 TRANSCEIVER CEIVER.

ELECTRIC PLANE MAGNET/C PLANE I I I I DIRECTIVE CHARACTER/S TIC FORSYSTEM INVENTOR ATTORNEY Jan. 13, 1948. A. c. BECK 2,434,253

DIRECTIVE CENTIMETRIC ANTENNA Fil'e'ci Aug. 21, 194:5 4 Sheets-Shet 2 5a r 42 a '1 i 39 40 +omscr1o- 0IREC7'ION 4/ I 43 TRANSCEIVER IN 5 N TOR,4.c. BECK ATTORNEY Jan. 13, 1948. A. c. BECK 2,434,253

DIRECTIVE CENTIMETRIC ANTENNA 'Filed Aug. 21, 1943 4 Sheets-Sheet 3 RELAIVE. FIE/:5-

1 Jr 1 I I 1 I 1 I +30" +56 +10 -aoa b- DIRECTIVE CHARACTER/ST]: FORJITSTE OFF/6.0

INVENTOR A. C. BE Ck Jan. 13, 1948. A. c. BECK DIRECTIVE CENTIMETRICANTENNA 4 Sheets-Sheet 4 Filed Aug. 21, 1943 TRANSCEIVER TRANSCf/VER rlm u E PLANE E m M DIRECTIVE CHIRACTERISTIC FOR SN'TEM 0F FIGJO WITH VANEOFF/6.10 WITHOUT VANE lNl EN TOR ATTORNEY Patented Jan. 13, 1948DIRECTIVE CENTIMETBIC ANTENNA Alfred C. Beck, Red Bank, N. J., assignorto Bell Telephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New York Application August 21, 1943,Serial No. 499,453

16 Claims. (Cl. 250-11) This invention relates to directive radiosystems and particularly to directive antennas especially adapted foruse in centimetric radar systems.

As is known, centimetric and decimetric waves having a wavelength,respectively, of one to ten centimeters and ten to one hundredcentimeters are now being used in radio directional and ranging (radar)systems. For waves of these microwave wavelengths the conventional priorart dipole-parabolic reflector antennas used with longer wavelengths arenot satisfactory, and it appears advantageous to obtain for use withmicrowaves more eficient antennas. More particularly, it now appearsdesirable to secure lobe switching radar antennas having a high gain andnegligible minor lobes and lobe sweeping antennas having a sharp majorlobe in the electric and magnetic planes.

It is one object of this invention to secure a highly directivemicrowave radar antenna.

It is another object of this invention to obtain highly efficient lobeswitching centimetric antennas and lobe sweeping centimetric antennas.

It is still another object of this invention to energize efficiently theentire line focus of a cylindrical parabolic reflector.

It is a further object of this invention to obtain a highly efficientradar antenna having narrow electric and magnetic plane lobes.

In accordance with one embodiment of the invention, the linear broadsideslot antenna of a leaky wave guide of the first kind is aligned with thefocal line of a parabolic reflector, the slot antenna and the focal linehaving equal lengths. In accordance with another embodiment, a linearbroadside slot antenna is positioned parallel to the focal line of aparabolic reflector and oscillated through a given angle for the purposeof obtaining a sweeping lobe. In accordance with still anotherembodiment, the focal line of a cylindrical parabolic reflector ispositioned parallel to, and included between, two linear aperture waveguide antennas, and a transceiver is connected alternately to theantennas whereby lobe switching is secured.

The above and other embodiments of the invention will be more fullyunderstood from a perusal of the following specification taken inconjunction with the drawing on which like reference characters denoteelements of similar function and on which:

Fig. 1 is a perspective view of a directive antenna constructed inaccordance with the invention and Fig. 2 illustrates the measureddirective characteristic for the antenna of Fig. 1;

Fig. 3 is a perspective view of another directive antenna of theinvention and Fig. 4 illustrates the measured directive characteristicfor the embodiment of Fig. 3;

Fig. 5 is a perspective view and Fig. 6 a diagrammatic sectional view ofa lobe switching 'sweeping antenna of the invention and Figs. 11

and 12 are measured directive characteristics used in explaining theembodiment of Fig. 10;

Fig. 13 is a perspective view of a different em-- bodiment of theinvention for securing lobe sweeping action.

Referring to Fig. 1, reference numerals l and 2 denote, respectively, atransceiver and a coaxial line connected thereto, the line having anouter conductor 3 and an inner conductor 4. Numeral 5 designates a Vleaky wave guide antenna comprising the branch wave guides or legs 6 andl and the stem or main wave guide section '8. Each branch guide containsa longitudinal slot antenna 9. The two slot antennas face each other andform an angle having a value, for example, 20 degrees, dependent uponthe phase velocity in guides 6 and l and such that maximum action occursalong the bisector of the aforesaid angle. The branch guides 6 and l andthe main guide 8 are each equipped with a reflective transverse end wallID. The inner conductor 4 of line 2 projects into the stem section 8 ina direction parallel to the a wall of section 8 so that the main guide 8and the branch guides 6 and l transmit and receive H11 waves polarizedhorizontally, that is, in a direction aligned with the transverse orshorter dimension of each of slots 9. As described so far, the structureconstitutes the well-known prior art V leaky pipe antenna. In accordancewith the invention, triangular metallic shield members II and I2 areprovided, each member being attached to corresponding b walls of the twobranch guides 6 and l. The two members II and I2 form a linear apertureantenna l3 having a longitudinal axis I l perpendicular to bisector l0and a transverse dimension or width l 5 greater than the width of eitherof slots 9. In other words, the members II and [2 function to transformthe two narrow slot antennas 9, each angularly related to bisector I0,into a wide aperture antenna I3 perpendicularly related to bisector I0.

In operation, Fig. 1, centimetric waves generated in the transceiver Iare supplied over line 2 to the guide section 8 and thence to the twolegs 6 and I, the wavelets conveyed in wave guide branches 6 and 1 anddelivered to the slot antennas 9 being horizontally polarized as shownby arrows I6. The wavelets emitted through the two slot antennas 9combine in phase, by reason of the critical angle between the slots *9,for the direction I! which is aligned with the bisector of the angleformed by the slot antennas '3. Stated differently, considering theverticalplane :containing the branch guides 6 and I and hereinafterdenoted th magnetic plane, maximum action occurs in the direction N.Considering the horizontal or the electric plane containing bisector Illand perpendicular to the magnetic plane, the triangular members I I andI2 function to prevent side radiation and in general .to produce.maximum action in direction II. In the case of reception, the reciprocaloperation obtains, as is well known, and echo waves reflected by adistant target are collected by the aperture antenna I3.

Referring to Fig. 2, curves I8 .and I9 illustrate, respectively, themagnetic plane and electric plane directive characteristics for thesystem of Fig.. 1. It will be observed that the maximum lobe 20 of themagnetic plane characteristic is relatively narrow, that is, about 7degrees wide at the half power point corresponding to 0.7 On the powersquare root scale. Also, beginning at points 2| and 22 'on curve I9corresponding, respectively, to the +25-degree and the .20. deg r'eedirections, the curve slopes downwardly at each end, so that sidewiseradiant action, as for example, radiation and reception in the+50-degree or 50- degree direction, is minimized.

Fig. 3 illustrates a structure comprising a cylindrical parabolicreflector having its line focus energized by the antenna of Fig. 1. Inmore detail, reference numeral 23 denotes a cylindrical parabolicreflector and numeral 24 designates the line focus of reflector 23. A Vleaky guide antenna equipped with triangular shields II and I2, asillustrated by Fig. 1, is Positioned so that the longitudinal axis I4 oflinear aperture antenna I3 is aligned with the focal line 24. Thereflector 23 and the focal line 24 have a length equal approximately tothe length of the aperture antenna I3. Numerals 25 and 26 denotesectoral end shields each extending between an extremity 21 (Fig. 1) ofthe aperture antenna I3 and the associated extremity 28 of the reflector23.

In operation, Fig. 3, microwaves emitted by the aperture antenna I3energize the entire line focus 24 of reflector 23 and, in the electricplane, an exceedingly sharp directive lobe 29, Fig. 4, is secured. Inthe case of reception the parabolic reflector functions to receive theecho waves and to energize the aperture antenna I3 throughout itslength. Considering the magnetic plane, the directive characteristic issimilar to the magnetic plane directive characteristic for the system ofFig. 1. In Fig. 4, reference numerals 30 and 3| denote the measuredmagnetic plane directive characteristics of the structure of Fig. 3 withand without the end-pieces 25 and 26, respectively. It will be notedfrom these two curves that in practice the end-pieces 25 and 26 functionto secure an improved magnetic plane characteristic .infismuch as theminor lobes 32 of curve 30 are smaller than the minor lobes 33 of curveSI, and the nulls 4 34 of curve 30 are deeper than the nulls 35 of curve33.

The lobe switching antenna of Figs. 5 and 6 comprises a cylindricalparabolic reflector 23, such as used in the system of Fig. 3, and twoV-shaped directive antennas 5 each equipped with triangular shieldmembers II and I2, as illustrated by Fig. 1. Therectangularapertureantennas I3 and the focal line 24 of the parabolic reflector areparallel to each other and the focal line 24 is included between the twoaperture antennas I3.

-Numera136 denotes the principal axis of the parabolic reflector. Thesectoral end-pieces 25 and 25 each extend between the transverse edges21 of :both'aperture antennas and the corresponding edge 28 of reflector23. The transceiver I is connected by coaxial line 2 to a main waveguide section '31 and to a wave guide switch 38 of the type disclosed inmy Patent 2,409,183 granted on October 15, 1946. The switch 38 comprisestwo detuning chambers 39, a partition 43, a rotatable vane 4I, twonear-end orifices 42 facing guide section 3] and two far-end orifices 42facing guide sections 8. One of the far-end orifices 42 connects theleft chamber 39 to section 8 of the left-hand antenna 5 and the otherorifice 42 connects the right chamber 39 to section 8 of the right-handantenna 5. The vane is continuously driven by means of a motor (notshown).

In operation, Fig. 5, the pulse energy generated in transceiver I issupplied over line 2, guide section 3.1 and switch 38 alternately to thetwo antennas 5. Since one aperture antenna I3 is positioned on the leftside, and the other on the right side, of theiocal line 24, thedirection of maximum radiant action is switched between two paths makingequal angles with the axis 35' of the reflector 23. Thus, referringtoFig. 6, with the left aperture I3 connected by switch 38 to thetransceiver I, maximum transmitting and receiv-- ing radiant actionoccurs in the right or minus direction 43 and with the right apertureconnected by switch 38 to transceiver I maximum transmitting andreceiving action occurs in the plus direction 44, these directionsmaking equal angles with the axis 36 of the reflector. As shown in Fig."I, the directive characteristic 45 for the system comprising thereflector 23 and the left aperture I3 is substantially the same as thedirective characteristic 46 for the system comprising the reflector 23and the right aperture I3. Moreover, each directive characteristic ishighly satisfactory since the nulls 41 are deep and since the minorlobes148 are relatively small. In connection with Fig. '7, it isimportant to note that the curves 45 and 46 illustrate separate anddistinct charac teristics and not different positions of the samecharacteristic. Stated briefly, the directive characteristic does notmove gradually from the position shown by curve 45 to that shown bycurve 46 but is switched or jumped from one position to the other. Inradar operation, with the axis 36, Figs. 6 and 7, aligned with thetarget, echo pulses having the same intensity are received by bothantennas, the intensity being 0.8 as indicated by reference numeral 49onthe vertical field scale, Fig. 7.

Referring to Fig. 8, which illustrates a lobe sweeping antenna'referencenumeral 50 denotes a leaky wave guide of the first kind having a pair oftransverse end reflective walls I0, .a longitudinal slot antenna 5| anda length of approximately o e-half avelength as measured in the guide.The guide 50 ispositioned so that the slot antenna 5| extends parallelto the focal line 24 of a cylindrical parabolic reflector 23, the focalline being included between the reflector 23 and the slot antenna 5|.The guide 50 is connected to the transceiver by a coaxial line 2 havinga rotatable junction or coupling 52 such as disclosed in my copendingapplication mentioned above. A shaft 53 is attached to the bottom ofguide 5| and is connected through the coupler 54 to motor 55. With motor55 operating, the coupler 54 functions to oscillate shaft 53 and slotantenna 5| through a predetermined angle, for example, 20 degrees, sothat the slot antenna 5| moves back and forth through the focal line 24,the angle being centered on the axis 36 of reflector 23. The meanposition for guide 50 is denoted by reference numeral 56.

In operation, Figs. 8 and 9, pulsed centimetric waves supplied over line2 from transceiver l are emitted through the slot antenna 5| in abroadside direction perpendicular to the plane of the slot 5| and arethen focussed by the reflector 23. Upon reflection by the distant targetthe wavelets collected by reflector 23 are supplied to the linear slotantenna 5| and thence conveyed to transceiver With the slot antenna 5|at the extreme right or plus position, Fig. 9, maximum radiation is inthe left or minus direction 51 and the major lobe of the directivecharacteristic has the position denoted by numeral 58. As the slotantenna 5| rotates to the left, the direction of maximum action movestoward the right. With the slot antenna 5| in the mean position thedirection of action is aligned with the reflector axis 36. When the slotantenna 5| is in the extreme left or minus position, maximum actionoccurs in the right or plus direction 59, the position of the major lobeof the directive characteristic being denoted by reference numeral 60.As indicated by the major lobe peaks 6|, 62 and 63, as slot antenna 5|oscillates the major lobe moves back and forth between the extremepositions 51 and 59, and radio scanning obtains.

The lobe sweeping system illustrated by Fig. 10 differs from that ofFig. 8 primarily in that the line 2 is connected to the mid-point 64 ofthe leaky guide and the leaky wave guide 5|] is maintained stationary.The lobe sweeping action is accomplished by means of an auxiliarymetallic reflector or vane .65 having the two parallel reflectorsurfaces 66 and 61. As in Fig. 8, numerals H3 denote end reflective wallmembers. Assuming the transverse magnetic plane dimension of the leakyguide 56, Fig. 10, is the same as that of the leaky guide 5|) of Fig. 8,the length of guide 50 of Fig. 10, as measured in wavelengths in theguide, is twice that of the guide 50 of Fig. 8. The shaft 53 associatedwith motor 55 extends longitudinally through vane 65 and, in operation,the vane is continuously rotated. The rotatable vane 65 is includedbetween the slot antenna 5| and the reflector 23; and the focal line 24is aligned with the slot antenna 5|.

In operation, Fig. 10, centimetric energy is supplied to and receivedfrom the slot antenna 5| by transceiver I over line 2. During one-halfrevolution of vane 65 the reflective or mirror side 66 faces the slotantenna 5| and an image slot antenna exists. With the transverse axis 68of vane 65 perpendicular to the axis 36 of the parabolic reflector 23,the image slot antenna is on the axis 36 as shown by reference numeral69, and with the transverse axis parallel to the axis 36 the imageantenna is absent, that is, the vane functions as if removed. As vane 65moves through one-half revolution the image antenna moves from theposition shown by numeral" through the focal line 24 to the positionshown by numeral H; and the couplet formed by the slot antenna 5| andits image makes one complete right-to-left sweep through an anglecentered on the axis 36. Consequently, the beam or lobe produced by thecombination or couplet comprising the stationary primary slot antennaand the moving image antenna formed by the vane makes one complete sweepfor one-half revolution of the vane 65. Similarly, during the remaininghalf-revolution, the reflector side 61 faces the slot antenna and thecouplet makes a complete sweep. Thus, there are as many sweeps perrevolution of shaft 53 as the number of reflective sides of vane 65. Ifvane 65 were four-sided, as in the structure illustrated by Fig. 13,four sweeps would be made during each revolution of shaft 53.

Referring to Fig. 11, curves 12 and 13 denote, respectively, themeasured electric (horizontal) and magnetic (vertical) plane directivecharacteristics for a structure constructed in accordance with Fig. 10,substantially, except that the vane 65 is omitted. As shown by thesecurves, maximum action for the system without vane 65 occurs in adirection aligned with the parabolic axis 36. The magnetic planecharacteristic comprises substantially only a .single lobe in view ofthe directive action of the slot antenna 5|; and the electric planecharacteristic comprises substantially only a single lobe by reason ofthe directive action of reflector 23.

Fig. 12 illustrates the measured lobe-sweeping characteristic of asystem constructed in accordance with Fig. 10 and including a rotatingvane. Thus, the maximum lobe 14 is at the left of axis 36 when thereflective side 66, or 61, of vanes 65 is oriented so that the imageantenna is at the right of axis 36 and in the position denoted bynumeral 10. When the reflective side 66, or 61, is positioned so thatthe image antenna is at the left of axis 3'5 and in the position denotedby numeral H, the maximum lobe 15 is at the right of axis 36.

Referring to Fig. 13, the lobe sweeping antenna is fundamentally thesame as that of Fig. 10, except that a corner reflector 16 of the typedisclosed in Patent 2,270,314 to J. D. Kraus, issued January 20, 1942,is used instead of a parabolic reflector and a four-sided auxiliaryplane reflector 11 is employed instead of a two-sided vane. The rotatingquadrilateral reflector 11 extends paral lel to the corner reflector andis included between the slot 5| and the corner reflector 16. Inoperation, the maximum transmitting lobe for the entire system makes onecomplete right-to-left sweep during a quarter-revolution of reflector11, that is, one sweep for each of the reflective sides 18.

Although the invention has been explained in connection with certainembodiments, it should be understood that it is not to be limited to theapparatus disclosed, inasmuch as other equipment may be employed inpracticing the invention.

What is claimed is:

1. A lobe sweeping antenna comprising a rectangular wave guide having alongitudinal slot antenna, a transceiver connected to said guide, andmeans for moving said guide about a longitudinal guide axis.

2. A lobe sweeping antenna comprising a rectangular wave guide having alongitudinal slot antenna, a transceiver connected to said guide,

means .for oscillating said guide about 'a longitudinal guide axis, anda .concave areflector facing said-slot antenna.

3. In combination, a-cylindrical'parabolic antennareflectorhavinglafocalline, a=wave guide having a longitudinal slotantenna extending parallel ,to said-focal .line and facing saidrefiector, a transceiverlconnected to saidguide, and means foroscillating said slot antenna.

4. In combination, a triangular wave; guide antenna :comprising :twozangularly related wave guideshaving longitudinalslotsfa'cing each otherand connectedto la -transceiver,-apair of triangu- 18.1";Sid815hi61dmembers each extendingbetween a pair of correspondent sides,of'saidguidea-said shield members forming a -linear aperture antennaextending perpendicular to :the bisector of the:angle.betweenSSJdwSlOtS.

5. In combination, a wave ;guide :antenna in accordance with :claim 4,and a cylindrical parabolic reflector having :its decal line ialignedwithsaid linear aperture antenna.

16. in combination, :a wave guide antenna :in accordance 'with claim .4,:azcylindrical parabolic reflector having a alength substantiallyequal-to the length o'fsaid aperture antenna .and a focal line alignedwith said .iinear iaperture antenna, and:-a pair of endlshield memberseach extending ibetween correspondent extremities of said apertureantenna ;and.rsaid :reflector.

at a given point to a translation device and -'having at "least one endreflecting '-wall, said pointand reflecting :wall being spaced :a halfof :a guide wavelength, whereby) the directly propagated :and reflectedenergies are cophasal.

10."In acombination;alcylindrical parabolic reflector having'alline'focus, a :wave guide having a longitudinal slot :antennalcoincident with-said 'focus, and a translation device connected 'tosa'id :guide.

11. 'In.cornbination,la(concave'reflectorihaving l a :line focus, a'smetallidwave :guide :having' at least .-one transverse reflectingwall, said guide having a longitudinal :slot :antenna facing -saidsrefiector, a translat-ion device connected athereto 8 at a-given point,the distance betweensaid point and said transverse well beingelectrically equal to-a half of a guide wavelength, whereby the wavesas-emitted or collected-at said .point and the waves as-reflected atsaidtransverse .wallare cophasal.

12. A'lobe'sweeping antenna system comprising a hollow reflector, awaveguide having a longitudinal slot antenna extending parallel 'to andfacing said reflectonatransceiver connected to said guide, a linearreflective vanepositioned parallel toand includedbetween said slotantenna and said reflector, and means 'for rotating said vane.

13. A lobe sweepingrantenna system in accordance with claim 12, saidreflector being a cylindrical parabolic reflector.

14. A lobe sweeping antennasystem in'accordance with-claim 12, said vanehaving two refleeting surfaces.

15. In'combination, a linear wave guide comprising apair'of transverseend reflective walls anda side wall extending therebetween, said side.wall containing-a slot antenna, the longitudinal dimension of saidguide being equal to a half wavelength -or a multiple thereof, asmeasured in the guide, said wavelength being dependent upon a'transversedimension of the guide, and a 'translation device connected to saidguide, Wherebysaid longitudinal dimension is dependent upon saidtransverse dimension and the phase velocity-oi said guide. and maximumtransmitting orreceiving actionoccurs in a'directionrperpenicular tosaid side wall.

16. In combination, a cylindricalzparabolicreflector having a focalline, a linear rectangular wave guide comprising a side wall containinga slot antenna, apairof transverse end reflective wall connected to theextremities of said side wall and spaced-a distance equal to awavelength as measured in the guide, and a translation device connectedto the mid-pointof said guide.

ALFRED 'C. 'BECK.

Name Date Southworth July 9. 1940 Clavier Oct. 24, 1933 Ilberg May 21,1935 Hansen June 25, 1946 FOREIGN PATENTS Country Date Great BritainOct. 15, 1931 Number Number

